Automatic antibackflow valve



Jan. 8, 1946. k SNYDER 2,392,782

AUTOMATI C ANTIBACKELOW VALVE Filed Sept. 19, 1942 2 Sheets-Sheet 1 27 auvs IINVENTOR; 4EOM/M Z 5/6 09 A Z} K Patented Jan. 8, 1946 UNITED STATES PATENT OFFICE,

' 2,392,782 "Q: I 2 AUTOMATIC AN'rmaoKFLow VALVE Leonard L. Snyder, Montebeilo','Calif. Application September 19, 1942,8erlal No. 458,930

8 Claims.

This invention relates to liquid flow systems and particularly pertains to an automatic antiback'flow valve.

In connection with liquid flow systems, such for example as those in which water is delivered from a water main through a connecting service pipe service line or supply line to the domestic lines of a building, or in cases where water is delivered in' the same manner to equipment in an industrial plant or to any private or domestic piping'system or fixtures or equipment thereon, occasions sometimes arise when the water pressure in the supply line and the water pressure in the domestic piping system becomes unbalanced so that a major pressure occurs in the domestic piping system. Under such conditions a backflow action will be created flowing reversely from the domestic service lines to the supply line, with the result that this water, now considered used. as well as polluted, contaminated, or containing deleterious matter, may be drawn into the domestic piping system, through the service line and into completely between said desired points therein at a time when either back-syphonage or backflow exists, whereby a reverse flow of water will be interrupted by said air chamber and be expelled toatmosphere, and thus have no opportunity to reach or enter any part or parts of the piping system that said device has been interposed to prevent. V

In some instances it has been found that a backfiow stream will be established through a check valve that remains wholly or partially open. In connection with check valves, bleeder valves have been provided to drain a portion of the backflowing liquid from the domestic service pipes or from between dual check valves. Some difllculty has been encountered'with this type of construction. First, for the reason'that under backflow conditions an outlet pressure of a value appreciably above that of the inlet pressure usually'exists before the 'bleeder valve will open and drain the liquid to atmosphere. In cases where a check valve leaks considerable water will backilow into the service main before the bleeder valve is opened, and it is even possible that the outlet pressure never exceeds the inlet pressure by an amount suflicient to open the bleeder valve, yet serious contamination may resultthrough the leaking check valves. Secondly, in some devices employlug-dual check valves it is found that a check valvemay stick. Thus, the valvewill be held 4 open and the backilow structure will not t uncwheresaid systems contain water from different sources or where onev supply system, often called the secondary, is. not under proper sanitary su,- pervision; These have in certain instancesproved objectionable due to the fact that aleakage at or through theflstructure or device of the backflowing water can occur without detection. This might be brought about by the failure of valves to seat; orby the fact that certainparts might become damaged or barrier walls ruptured within the valvestructure itself. It is the. principal object 01 the present invention, therefore, to. provide automatic means which will act to interrupt the backfiow and, back-syphonage of water from the domestic lines to the supply line or between water served fixtures, devices, icont'ainers', [recap-'- tacles or equipment and the domestic or supply piping system, or between inter connected supply systems or ditlerent origin, or between, any parts or areas 01 either supply linesor domestic service lines as maybe desired,- and inaddition thereto tion. 'It has also been found that where a small valve leakvocc'urs within a domestic piping system,

this small and continuous stream of liquid will flow across the valve seat and erode or wire-draw the'seat to-prevent a complete seal;

In the devices previously discussed the opening and closing of thej valveshas been produced directly by an appreciable change 0! pressures on the opposite'sides of the device. Devices de-i pending on this operating force have not been positive in their action, audit is the principal object in designing this structure to provide an anti-backflow valve which will be simplejin its construction and will operate positively and directl inrespons'e to a relatively small variation in liquid pressure and with aminimum amount of resistance to the normal flow of liquid through the device when the valves are open.

The present invention contemplates the provisionoi a valve housing adapted to be disposed directly in the; line or flow from a'supply line to a domestic piping system, and which structure is fitted with positively actuatted cut-oil valves and a positively actuated bleeder valve, the said valves being moved toseated and unseated positions by means responsive to a. relatively minute'pressure differential on opposite sides of the device.

In'this specification the term supply or service a line" indicates any induction connection, and the term domestic piping system indicates any eduction connection.

The invention is illustrated by way of example in the accompanyingdrawings in which:

tical section showing one form of valve unit with Figure liiS a emerged view' in-central t er fi to reciprocate.

3,392,73 7 v V I Z 4 I. 1

cylinder 35 is a cylinder plate 31 which is cen trally threaded to receive the domestic line ll connected with a domestic piping system. The cylinder 35 is formed with a central bore 38 within which a piston structure 39 is mounted The piston structure includes a. sealing-disc 48 mounted upon a piston rod 4|. This disc is held by a cup 42 which is formed with radial fins 43. The finshand the cup are made of metal: so: thatthey will act .as-zguidesfor the piston structure. Mountedbn the outer end of' which the present invention is concerned witn eth piston r d s a n av d p sto up 44 which the valve elements in their normally opened po' "isseoured in p i n p n t p t n rod 4| by sitions. .l'fL L-il 1C1; fifi'nntsifi'i'r ll'heicup 44 as well as the packing Fig. 2 is an enlarged view in central .vertical.15 i he Q aronr f rably mad of non-metallic section showing one form of valve unit"wit which the present invention .is-concernethwith the 3 l valve elements in the position assumed ,when a condition of backflow takes place.

:Eis: 131s an enlareedcvi m in mant wo t alsectioni-showingrazmodi fk q m OfM JVBYa 'W Y' ment operated by positive. mechanical means.

rReierrin imo oenart u arly-Jto th adrawinsai 7 l0: indicates;a :pi-pe connected with p a service line.- n-p pe fliform p rteofit e: domestic pip system a nd .is; ShOWIljiIl-i Fig; l as. heingin longi tudinal alignment with-pipe l9. Interposed:. be-- een th se'zt o-ep e s a ganti-bao fio valve structureI2; with which.- the-present invention: i

7 h i. MN m h *v ;v u tu rino u s a se vice valv s ar i ular r o cern do s a; 1 in d es i alv housi Mi i n; intermediate solenoid. nn-it ,The service valve ou in s f t e t i s, outer end itha oss. which-, isformedwithra central pore IL. {The outer nd-oi th s ore s h aded a e ve-th vic p p h v' io d und the/inner ndioiat e n "i n annularv lv ss ti flw o is ub- "a e @i j sui ibsd b ui rrt h l r we 25 ,The cap screws .zleengage threaded Lia e h teinally threaded 78 16 ,receives 'a noii-im agpeti tubular core-jflffupon-which:th winding 05E; a

and {thus provides a complete; housing' for solenoidlco'il 3T androrming 'whatli as. an

m ss n si ih a p i e "i sio i V eeve lil",ClfheIsIeeveZEbVrIapS l the eneumferent' 1 edges off the'discsjii'landjl r e lr aiie in ro s-s i nae it r a materiaL'suclFas rubber for example. The cup euaren a. purpose tohe' hereinafter described." V

The. sealing. disc All: rests normally against. .an inwardly projecting annular valve seatv "41 I formed. updnztheinnerend wallliifl .ofithefi linderii A central ore 49 isiormedjthroughlthe'wallandis circiimscrihed 'by the vane: seat 1U The piston rod" i f 'is connectedjtoithe end epicentr .a valve plunger 5'1". .Thejvalvei'plungerlfilfis formediwith a slidingifitfwithiri the tubular core 3lllandfrecipe rocatesilbngitndifn'ally therein; Y portion 7 onthe pln'nger isi cylindrical'r asindicated at 52; It is urged eo'iitwardlyftoward the .domesticline l I? by ailspringl 53jjw ichlis interposed] hetweenzla carries a, valve disc '5fij'which 'm'ay come to. restv .oneninesi ngtne end' discj23fandhold the f valve; housing},1.3 concentricallywith relati'o ciirni unieatesj witn i QQ'nical'g-shape' througnzf Bytfhisar Ye i sides oittlie m'emberIEBiandicommuniGate Twithfa V centralpassagewayfiil through tn valveplimger;

rhej'nisegas is heldfin Osman. by ca sc ev at wni gn a afetmgn eadliif proiectingir'ito'the bore flofthe'hous lsgimne essaeewafla 'agew zstf "fies as c j li 'i m y-flow; at r wnicnjit may: pass thro gh nowopenness: iji 1 h) idr' sca e-then; new intolaeresjtricted whichfi fcrniedinaplate raining. mete rece t-tea e uterrend of the I shoulder 54.;011 tn plunger and the a'seavsai 88 may slidethrough anliopening 18 in the lug=8.1. This allows relative movement betweenthe lug 81 and the valve." -A nut 88 is provlded i'or the bol't so that when the plunger. I.moves in a counter direction the bleeder valve-will be drawn 'aiiva from itsseat. v

r The solenoid unit I5 is intended to beenergized by fluid pressure'responsive means. -This in cludes a bypass tube 8I which connects with a duct 82 leading'through the wall of the bossfl8" and communicating with the bore I1. Thus,- water from=the service line mayiiow into thetube 8I.- The tube is connected to leg 83 of a; U- tube 84. A leg 85 of the U-tube connects with a tube 88 which is in communication with the bore 38 of cylinder'35 through a duct 81. TheU-tube 841s partially filled with mercury, and floating upon the mercury in leg 83 of the U-tube is a ball 88. Disposed on the mercury in leg 85 of the U-tube-is a ball '89. These balls'are*preferably* made of rubber and will float on themercury as its level changes in response tovariation in'pressure in pipes I8 and I I. Mounted at the upper end of the leg is a valve opening and seat 98 which may be encountered by the ball 88. Mounted in the upper leg 85 of the'U-tube is a valve andseat 8| which may be encountered by the ball 88.

Thus, when the balls 88 and 83 move to extreme positions they will encounter their respective valve seats and limit further movement of the mercury in the U-tube. Since mercury is a conductor of electricity, it is;

used in this case to make and break an electric" circuit; This is done by providing a" connection 92 to an electrode 93 extending through the wall of the U-tube leg 83 and a'conductor 94 connected to an electrode 85 extending through the wall of the leg 85 of the U-tube. The conductor 82' leads to one pole of the solenoid coil 3i. The conductor 34 connects with an electric Ieed' wire 98. The conductor 88 connects to one pole of a source of electrical energy 91. The other pole connects to conductor 92. The horizontal level of the electrodes 93 and 85 are'so disposed as to insure that when the level of the column of mere cury of the leg 83 of the U-tube is lowered from a point of contact with the electrode 83 the electric circuit through the solenoid coil will be broken,

and when the level of the mercury contacts this electrode the solenoid circuit will be closed to cause the solenoid coil to be energized, for a purpose to be hereinafter described. I

In the form of the invention shown in Figs: 1

and 2 the difierenceof level of columns of mercury in a 'U-tube make circuit. 7 V V 7 Referring particularly to Fig. 4 of the drawings, a valve structure is shown which is similar to that shown in Figs. land 2 save for the'iact that the solenoid is eliminated and other operating means is provided. In this structure a housing cylinder I 2I is provided. A threaded bore I22 isjformed in one end of the cylinder and receives a nipple I23.

and break an electric formed around the inner end of the threaded bore for" the pipe I8. Adapted to seat againstythe by a"capscrew 'I21 having a-conical head I28 which extends into the bore of the nipple: Passageways I29 are'tormed' in 'thesldes of the plunger I28 and communicate with'longitudinally extending passageways-138 throughlwhich liquidmavilow. Thepassageways iIIll. are=-f rovided The nipple I23is internally threaded to receive'the service pipe I8. A valve seat I24 is which reciprocates within a cylinder I34. .The

cylinderi34 is threaded into the end of the cyl-fl inder I2I 'and-is providedwith a nipple I'35-which is internallythreadedlto receive the domesticpipa II. Atubular extension I38is formed integral with the cylinder I2I and is disposed with its axis at right angles ;to the longitudinalaxis of the It is preferable that this "extension;

ries a valve; seat I381 Extending through the nipple and'guided by a hearing I 381s a valve stem. a I 48 which carries a valve element I4I.

her in the event thereis any leakage of .water around the valve I32 or valve seat I24. Aspring I42 acts to normally hold thevalve I on its seat.

A finger I43 rests against the end of the valve stem I48'and acts. in opposition to the spring to lift the valve. This finger is carried by a lever I44 pivoted to the housing structure I2I upon a pin I45. The free end of the lever is provided with a pivot I48 which is secured to a shacklelink I41. .The opposite end of the link is engagedby' a pivot pin --I48 which secures it to a shift lever I49. cThe shifting lever I48 is formed with a ball I58mounted-within a seat I5I. The lever has a lever arm I52 which is pivotally engaged by the pivot pin I48 on one side of the ball and a lever I53which is disposed on the opposite side of the ball. At the free end of the lever I53 is a balli54 mounted within a socket I55 which is formed in the upper side of the valve plunger I26. A ilexible packing disc-is associated with the ball I58 to prevent a leakage of fluid from the cylinder I2I.

Connected to the lever I52 and the shackle I41 by a pivot pin I48 is a piston rod I58; This is conket. An electric motor I 58=drives this structure and is suppliedwith'electricity through suitable conductors. 7 7 In operation of the form of the invention shown in Figs. 1 and2 the valve structure I2 is inter posed between the service pipe I8 and the domestic pipe II, and when this structure is in open position; asshown in Fig. 1, thewa'ter ,irom'the" pipe I8 maypass throughrthe bore I1 infthe housing-I3, and then around the end of the valve disc 58,after which it will flow through the ports 58 and into the passageways 59 and 82.

which lead through the valve plunger '5I, andthence through the openings 83 to the chamber fqrr'ned-inthe housing portion 38. The water then flows throughthe bore 48in the'domestic valve housing I4 and then around the cupjf which is carried as a part of the piston valvestructure 38. -Due to the flexibility of the marginaledge of the cup 44 the water willbe tree to pass'around the cup 44 and through-the bore of the cylinder 38 to the domestic line II. The

spring53 will maintain the plunger 5|; in its moVedposition, as-shown in Fig. l, andf'-thus make it possible ior' a' flow oiwater to" V A threaded nipple I31 is screwedinto this extension and car-' domestic line ihe mercury in :the U inf direetroiriiomthegseme use mewtheatremeshe -line I L? 1 Item-1:1 elsobeievident that so longthere is a ontinuous noiimal fidw of liquid" fromth pipe to to the pipe l l there' -would be aetendency forf the valves" tomemaini: open ieven though the s'pringbecame inoperative litters- 'tion is directed to mes-mes that when the plung'm V normal.rspacezbetweenfthzdisa 6$andithlugl i't i zigreater athaninthe alengthtof travels oi: the we:

1 the; i8 1: wilt actitm comp'rssi umlihold'iithe m I 'nto: itsivseat'izll *vwith'iconslderable The per surexof water: in the pipesgl 0 snot: l 'l' is eq uat :or: when thezpres'sure ofnawaterzirr piper I6 is greater thainz-the pressure in pipe: tt,..-an-a1su= @01 course when'the flow of water' thmughv:theistructureis; in 'therdirections from the; service line A H! std: thi

Attention is directed "particularly :toitheehtion; o1 theipiston 1 39; and. its Gulf-44? It -willfbeisee'm' that-the. cup; is: :concavedmnthe; eductioni'side of thewhousing; and; that itslaedg eis relativelyvthin; Attention is alsondirectectztm the-{fact that by pass-ports: '46:"31'8 formed througli'it';v Thus-the; flared lip; of the cup;may be easilyfiexedzto mit-the i-flow of water from ;the rhousihgirto-rthe: eduction side: and willbeforced outwardly-with? aa. relatively small fluid: pressure to engage the;

rwall when; backfiow occurs; ,The .cup fis not sufis ficiently rigid to .,.create:-a. fluid seaL -aget-1 nst-ex cessive beckfiow pres-surei. Its purpose is -to' .018?

ate sufiicienti bac-kfiow pressure through the-tube 85am insure actuation of; the: fluid; pressure re;-

withpqsitivepnd direct means; for preventing:

the level willbeestablishechby theamount ofipressure v rdifierential between the .fiuiti.v 1o" Pipes [Iran d; H: and the level-'wi1l .be. higheninsleg 85 than in leg 83.: On .baJckfloW this conditioniwlll be. reverseci; Insome instances it 'bevde pl 1; 1 ;snge the valve .to :cause it to openatewhen the pressure-in pipe llisbelow-the pres sure in -pipe 10-. This'cansbe donerb-y lowering:

the. contact position: of;[electr0de '92; By-this alg r'ang ement additional safety can be, insured when:

7 V abackflow-eo elition is extremely hazardous.

electrode 95; is in continuous contact with the M etube M and-the electredevsa is normally; out of contact 5 with the merourx; in the :leg. :83 of ther-U:-tube :so that the; circuit to, the

I solenoid-c0113] is-broken-normally; the'eveht,-, however; that the pressure: of {liquid in the :tubes; 8}; am} 85 becomes ,unpalanced soithaethe egres thzittheeliquidir'mtober flfi. awillapassidownwardly,

it imlegrflit. ltwi'l'lherrecognized thatxztheamount:

' minute difierence in pressure will bring :themer-j ates"tithena csnesiseumsits previously described, wil'llfuncti'omwherrthe zpres+ cury, hr legt83- intmcontact with the electrodei93 V and: close the. oi-rcuit-through conductors; 92- -anl5 84 toaenersizethe coil 3 l-. This will alct-toretractj the plunger: 5% and move.Z;the-,-valve elementsfllh andigifi onto the valve seats 1 1 and l 8,-;rrespe V- tivelys; #Ihus; theaflowvofvwater will be; positively interruptect atwtwo points; so that-the water cam:- notibackflow from-the gdomestic; pipe I l and int o the housing section -,3;6- and'into orv through the passa ewa s o medlt sh the l n er 5. S r; mukt ne u l wi hi-t s' e tion: e usrfi' c -s f i'byg h h se i lb r tra t d; Qi a 9 siti'o where it will positivel y -engagesthe ;nut 89; an pull .r-the valveldisc v of? its seat H Ems-- e mitanrli u d w i a be nini the housing ;section;-3B;t odrain orbleetiefr om the housing, tthroughg thepassageway ,1; :into the;

' bleeder pipe15s It willelsosbe recognisedethagt shoulgig there beans; leakage: erounclsthe, valve. 33' and, over theevalver seat. M this: will dreinv ofi through-thebleeder pipe liend will'have noop portunity to reach the! passageway {through the 2 hand plunger L Attention.isldirecteqjtothe f act thet vilhemthe. plunger 5 Lmoves away, from. theuendj face of the cylliider headAfijhreiptovided. agap so. that leakage. water Wouldljs'pill over, the edges of the; bore -43 o'ri'cl pass downwardlyfto froml thelhousing. through the bledrs pipe eve'nt that' excessive ,differentiall pres sure' eitistslins elther direction between the (pipes;

vent. the.lossfoflrnercury in. the, tubes 8 stor es v gWhen the proper; balance of pressure -has been re.'.-'establi shed v lb'etween the? liquid; the servioei s on iv meansam w n I p pipegllliahdithe liquidrinithen-domesticlpipefl l The present inventioni-s cohcerned additionally: the A; e'rcury. in ether legs Athena- 8'5, o'filtheluttubes; will be restoredl toh heirlhormelllpositionh Teiswm' nt i uptthe; flow;ofllelectriccurrentg to thelcoilfi leandflwlll. permit; thesprin g 5.3.150 x valve discs mime SfifromJtheir. seatsso that a normal flow of will oocur.

nquie .t iroqghfth contr umt gt Cformof v the in sttm shtwii minim;

Q5 ths-{strudtureloperates ongthe same principle static conditiorr. Under norrrlztifiow{conditioris thelle vepllflt shown in Figs. 1 and 2. When the electriezoit ouitr-Vtol the (motor 58 is. completed l the motor drives therZthrusitosk-lfl, zforcing the; rod Al 565 1201 vile-rid, thedefit as} viewed; in Figure 4-, aotuating; 'c'e-theovalves; I fiend-J Slonto; their-correspon ngiseatslfl This; action u zilLelso: swing theleverr Mite li ftthebleedenvalye I445 I Attentionrisldirectedl, to theefact that -the -pis-,; io e n A d .3 rwe Mme-w h? relatively-small bypass: duct 46.; flhis portper mit se "utilization of pressure iaroun dl the oup s flier-M e r l. V opehinss, hrough the-valveseatsflByandAl supah ie is ase -5 a es:-= he lvewill c s 79 baxlsrreedfve-ltz and awvery small excesssingpre 7 sme-i inlrserviceepipe. I-fliwillzzcausei:theephmgrto move;- to ainormal flows-position: If-"these; holes ofsohansedm level 'caniibewvery :slight -isothataw immed action will simultaneously; move -(the 4 39 hats, seetei-f-end V by ma kinggith .t sla ea n the ,c lindei' it; whic isseel d by the-cupsfland J3 s muq a ee t an th a .through valve seats I H and j 24, excessive pressure would "have to bebuilt-up in thelservice pipe I that in bygwater-hammer will not, operateto close the 1 vvalve, buta steady rise -in outlet pressure above inlet pressure, although of only a, few seconds duration, would close the switch and: operate the valve. 1 g

Itwill thus be seen that the backflow prevention valve units here disclosed are simple, and rugged in construction; and provide? for a direct stream flow oi liquid from the service line to the domestic line with rapid positively acting means for closing valves'to prevent backflow, thus insur- 1,; ing that the valve will operate with great precision and with a minimum friction loss due to the flow of water through the structure.

While I have shown the preferred form of my invention as now known to me, it will be understood that various changes may be made in combination, construction and arrangement of parts by those skilled in the art, without departing from the spirit oi my invention as claimed.

Having thus described my invention, what I lalm and desire to secure by Letters Patent is:

1. In combination with an inflow pipe and an outflow pipe disposed in substantial longitudinal alignment, a backflow prevention valve housing therebetween and with which the contiguous ends of said pipes communicate, an inflow valve seat, an outflow valve seat within said housing and in substantial longitudinal alignment with each other and the pipes, a valve for each of said seats, means connecting said valves so that they will move in unison toward and away from their seats, means acting to thus move said valves, and fluid responsive means communicating with the inlet and outlet pipes at points beyond their seats and, whereby a differential pressure between the fluid in the inlet and outlet pipes will initiate movement of said valve operating means tending to move both of said valves to a seated position when the inflow fluid pressure is less than the outflow fluid pressure.

2. The structure of claim 1 including an outlet opening in said housing to the atmosphere between the inflow and outflow opening, a valve for said outlet opening, and connecting means between the latter said valve and the two firstmentioned valves arranged so that when the firstmentioned valves are opened the latter mentioned valve will be closed and so that when the first-mentioned valves are closed the lattermentioned valve will be open.

3. In combination with a service pipe and a domestic pipe disposed in substantially longitudinal alignment, a backflow prevention valve housing interposed therebetween and connected therewith and through which housing fluid may flow from the service line to the domestic line, a service valve seat within the housing adjacent to the service line, a domestic valve seat within the housing adjacent to the domestic line, a service valve adapted to rest upon the service valve seat, a domestic valve adapted to rest upon the domestic valve seat, means rigidly connecting said valves together so that they may move simultaneously toward and away from their seats and so that when said valvesgare in their oDeuPQ ition a continuous flow ,gi, fluid may take place betweenthe service and. domestic pipes, and the said valves opening in the: direction (i flow from with theatmoSphere, a bleeder valve v. ior openin and cl o si ng said bleeder alve opening'aconnection between the bleeder; valve and the service .and domestic valves and spacing the' same so that thebleeder valve, will be opened; when the service and domestic valves arelcldsedandfclosed when the service and domestic vanes-ere open,

. mean's yieldably holding-the service fanddoiiiestic valvesoftof theirs'eats uhderfii" in re ients conditions,-means pe iuve yitetfiaungtne service and domestic valve's'to "movstiiemyontc their seats to hold them,v eated, fluid ,pre'ssure'meang responsive toapredetermined differential in fluid pressure within the two lines to initiate and interrupt the operation of the valve moving means and whereby the relief valve is moved to open position when the fluid pressure in the domestic line approaches the fluid pressure within the service line within the pressure differential.

4. An anti-backflow valve including a housing having inlet and outlet fluid conduits and an inlet and an outlet port, a flow chamber therethrough, a movable plunger in said housing carrying inlet and outlet valves, a solenoid for moving the same, a diiferential manometer responsive to pressure in the supply and domestic conduits at points beyond said inlet and outlet ports, an electrical circuit including said solenoid operably connected through the liquid in said manometer so that a fluid pressure in the domestic conduit in excess of the fluid pressure in the supply conduit will close the electrical circuit and energize the solenoid to move the valves to a closed position.

5. The structure of claim 4 including a relief valve located in the flow chamber between the inlet and outlet ports and operably connected to move with the plunger, said relief valve to be urged toward a closed position when the plunger has moved to open the inlet and outlet ports, and means connecting the relief valve with the plunger so that the relief valve is opened when the plunger is moved to position to close the inlet and outlet ports.

6. In combination with an induction and an eduotion pipe, a housing connecting the same formed with a chamber through which fluid may fiow, a dual valve structure in said housing for interrupting the flow of fluid between the pipes.

the dual valve structure including spaced valve members connected together so that they will move in unison, separate valve seats adjacent the opposite ends of said housing and toward and away from which said dual valve structure moves in unison, a fluid outlet from the housing between the valve seats, a relief valve normally closing said outlet when the valves of the dual valve structure are in an open position and moving with the dual valve structure to an open position when the dual valves are closed, fluid pressure responsive-means, conduits connecting the induction pipe with the fluid pressure responsive means and connecting the eduction line with the fluid pressure responsive means in opposition 

